The present invention relates to a latch device used, for example, when a movable member such as a lid and so on is detachably engaged with a box-like base member, and formed of a push-push engagement mechanism (this can be referred to as a push-lock and push-open mechanism), wherein a striker is engaged by the first pushing operation, and is released by the next pushing operation.
FIGS. 8(a)-8(b) and 9 are latch devices disclosed in Japanese Utility Model Publication No. 61-163870 (FIGS. 1-8) and Japanese Patent No. 3126992 (FIGS. 1-12). Each latch device 70, 80, for example, is attached to a box-like base member 60, and is formed of a push-and-push engagement mechanism which engages a striker 62 provided on a movable member 61 when the movable member 61 is moved from an open position to a closed position, and releases the engagement by a next pushing operation of the movable member 61. In these mechanisms, the latch device 70 in FIGS. 8(a)-8(b) is a fundamental embodiment of the push-and-push engagement mechanism, and formed of a case 71, a latch member 72, a spring member 75, a pin member 76 for tracing, and a leaf spring 77.
The latch member 72 includes a heart-shaped cam groove 73 and an elastic engagement portion 74, and is urged and moved in a case projecting direction with an urging force of the spring member 75 relative to the case 71. An edge of the pin member 76 projects to the cam groove 73 in a state where the base end is engaged at the bottom face inside the case. The leaf spring 77 is fixed on the case 71, and an end side presses the pin member 76 through an opening 71a to secure the pressure force of the pin member 76 relative to the cam groove 73.
Also, the cam groove 73, in FIG. 8(a), includes a guidance groove 73a extending to the upper left side from the bottom; a guidance groove 73b for engagement and a guidance groove 73d for release, which are located on the upper side of the guidance groove 73a and parting right and left; an engagement groove 73c located at the bottom between the guidance grooves 73b, 73d; and a return groove 73e extending to the bottom from the guidance groove 73d. The elastic engagement portion 74 includes a claw portion 74a on the edge.
When the latch member 72 is pushed by the striker 62, the elastic engagement portion 74 is pulled into the case 71 by elastic displacement. The claw portion 74a passes through the claw portion 62a of the striker 62, and the edge of the pin member 76 is engaged in the engagement groove 73c. When the latch member 72 is pushed again by the striker 62, the engagement is released by the edge of the pin member 76 entering to the return groove 73e from the guidance groove 73d. 
The latch device 80 in FIG. 9 includes a case 81, a latch member 82, a spring member 85, and a pin member 86 for tracing. The latch member 82 includes heart-shaped cain grooves 83A, 83B on both bottom sides (front and back of the sheet of the drawing), and a pair of elastic engagement portions 84 on the upper side, and is urged and moved in a case projecting direction with an urging force of the spring member 85 relative to the case 81. Both cam grooves 83A, 83B have a roughly heart shape as a whole similar to the cam groove 73, but they are shaped differently. The pin member 86 is generally U-shaped, and the intermediate portion 86a of the U-shape is fixed on the inner bottom face of the case 81. Also, the edges 86b on both sides of the U-shape are bent inwardly to project into the corresponding cam grooves 83A, 83B.
The latch device 80 has a configuration such that an engagement force is increased by providing a pair of the cam grooves 83A, 83B relative to the device 70. Also, the edges 86b of the pin member 86 abut against groove side faces of the cam grooves 83A, 83B and trace along the different-shaped cam grooves 83A, 83B in a non-contact state with the groove bottom faces of the cam grooves 83A, 83B. The pin member 86 is moved in one direction of the cam grooves by providing a torsion force and eliminating the torsion force.
Relative to the device 70 in FIGS. 8(a)-8(b), the latch device 80 in FIG. 9 is superior in increasing the engagement force by a pair of the cam grooves 83A, 83B, and being able to control the frictional wearing of each portion or reduce the operating sound when the operation is switched because edges 86b of the pin member 86 are held in the non-contact state with the groove bottom faces of the cam grooves 83A, 83B.
However, it is not yet completely satisfied from the following perspective. Namely, in the device structure, the intermediate portion 86a is fixed onto the bottom face inside the case, and a stress received from the edges 86b is stored as a torsion force and eliminated, so that the operating sound can not be completely eliminated when the operation is switched, or the edges of the pin are forcibly deformed. Also, since the edges 86b at both sides are projected to the different-shaped cam grooves 83A, 83B, the value of the torsion force of the pin member 86 becomes easily changed due to dimensional errors of the projections of the pin edges 86b, etc., so that the stability of the operation is lacking.
The present invention has been made in order to solve the above mentioned problems, and the object of the invention is to provide a latch device, wherein an engagement force is increased by a pair of cam grooves to be able to keep a stable operation over a long period of time while reducing an operational sound and the load on the pin member.
Another object of the invention is to provide a latch device while improving the molding ability and appearance as compared to the conventional structure.
Further objects and advantages of the invention will be apparent from the following description of the invention.